Continued economic pressure in the marketplace for cans for the containment of carbonated beverages and the like has led to lighter and lighter weight construction of beverage cans. In particular, the side walls of the cans now being manufactured are thinner than ever and are consequently less durable. Difficulty is particularly encountered in counterpressure filling of cans, according to which the can is first filled with pressurized gas, and then with the carbonated liquid, so that the carbonation of the liquid does not escape upon filling. This requires that the can be sealed to the counterpressure filling valve. This is typically done by simply pressing the open end of the can into engagement with a circular resilient sealing member. However, the endloading required to effect a good seal of the counterpressure gas, which is usually at about 40 psi, is substantial, on the order of a hundred pounds. Accordingly, some percentage of the cans is ordinarily crushed. With the trend towards lighter and lighter can construction, this percentage can be expected to increase.
Most modern thin walled cans are flanged at the open end. The flange is usually formed by a lip which extends perpendicularly outward from the can. The substantial endloading caused by prior art counterpressure filling valves often caused damage and deformation of the flange since the force of endloading causes an axial deflecting moment on the flange at the perpendicular bend between the cylinder of the can and the lip. It should be noted that the flanged opening of the can is conversely relatively strong in the radial direction since the lip of the flange is approximately ten times thicker in the radial direction than in the axial direction.
Prior art attempts to obviate these problems have been unduly complex. For example, U.S. Pat. No. 3,519,035--Remane reveals a dosing device intended to be used with low temperature liquids such as liquified butane or propane. This reference discloses a filling valve which is actuated by an upward force exerted by the open end of the can or container upon the lower portion of the valve. This upward pressure is of necessity greater than the pressure required to simply support the fully fluid filled can. That is, it is necessary to maintain an upward pressure on the open end of the can in excess of the pressure required merely to hold the can in proper position during filling. Avoidance of this excessive pressure or loading is one object of the present invention. The Remane reference also discloses a sealing device comprising a tube which is inflated by an external source of pressurized gas. Expansion of the inflatable tube of Remane effects a seal on the inner diameter of the container rather than on the flanged opened end of the container. The prior art, as disclosed by Remane, thus utilized a complex two gas system that did not eliminate excessive endloading or take advantage of the relatively strong flanged open end of the container. A need, therefore, exists in the art for a relatively simple counterpressure filling valve which will provide a good seal against the escape of the counterpressure gas and the carbonated liquid, eliminate significant endloading of the can, and utilize the relatively strong flanged end of the can to make the seal.
As is well understood in the art, after filling of a can with a carbonated liquid, the head space at the top of the can, i.e. that portion of the can which is not filled with liquid, is filled with compressed gas. This must be vented to atmosphere in a so-called "snift" operation prior to removal of the can from the valve if excessive foaming and loss of product is to be avoided. In the valve shown in U.S. Pat. No. 4,442,873 this problem is solved by relative movement of the can with respect to the valve prior to cessation of the seal therebetween, such that the head space is increased sufficiently that no snift valve or the like is required. It is an object of the present invention to preserve this feature of the invention shown in the co-pending application, while forming the seal between the valve and the can without excess endloading, again so that the number of cans destroyed in the canning operation is reduced.